Inspection and maintenance are key factors for making sure that your biofiltration box is performing as designed and achieving the required water quality standards. Here are a few things to keep in mind...
1. Protection from Construction Debris
Bioretention box soil must be protected from compaction by heavy equipment traffic during construction. They should also not be used as material staging areas. Construction runoff should not be routed to the facilities to avoid fouling or clogging. Preferably biofilter areas should be completely covered until construction activity has ended.
2. Inspection and Maintenance
Pretreatment is suggested where high pollutant load generation is expected, for example, high pedestrian or vehicular traffic areas, areas with construction activity, moderate to high slopes, and sites with erosive soils. A higher inspection and minor maintenance frequency should be expected for these sites or where aggressive design infiltration rates are used. Accumulated sediment and debris, flow patterns, vegetation health and overall facility condition should be assessed every 2-4 weeks during the wet season or after large events. A routine maintenance plan can be customized for the site based on a 1 to 2 year observation history.
Flow line along the curb and inlet condition should be assessed routinely to make sure that flows are entering the facility as designed. Channels may form that short circuit flow paths within the biofilter, especially where it contains multiple cells separated by check dams or where the high flow bypass is within or downstream of the biofilter.
3. Minor Maintenance
Minor maintenance may be performed at the time of inspection. Typical activities include removing accumulated sediment, trash and debris from the inlets and surface of the bed. Regeneration of the biofilter’s hydraulic capacity may also require raking, and replacement of the top layer of mulch and/or soil. Exposed woven geotextiles should be covered. If a system has an overflow bypass within the vegetated filter bed area, debris may need to be removed.
4. Major Maintenance
If the biofilter is sized to hold and infiltrate a water quality volume, the presence of standing water after the design drawdown period indicates that maintenance is required. Higher rate flow-through designs with a relatively small pool volume should drain quickly. The infiltration rate of the soil should be measured directly and major maintenance should occur when the infiltration rate drops below the design rate. If minor maintenance does not return hydraulic capacity to the design rate, replacement of the soil, vegetation and drain rock may be needed.